NRF52820-QDAA-R datasheet(328/437 Pages) NORDIC

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Peripherals

ADDR

M-1

Stretch

Figure 125: The TWI slave responding to a write command

6.23.4 Master repeated start sequence

An example of a repeated start sequence is one in which the TWI master writes two bytes to the slave

followed by reading four bytes from the slave.

This is illustrated in the following figure.

In this example, the receiver does not know what the master wants to read in advance. This information

is in the first two received bytes of the write in the repeated start sequence. To guarantee that the CPU is

able to process the received data before the TWI slave starts to reply to the read command, the SUSPEND

task is triggered via a shortcut from the READ event generated when the read command is received. When

the CPU has processed the incoming data and prepared the correct data response, the CPU will resume

the transaction by triggering the RESUME task.

ADDR

Figure 126: Repeated start sequence

6.23.5 Terminating an ongoing TWI transaction

In some situations, e.g. if the external TWI master is not responding correctly, it may be required to

terminate an ongoing transaction.

This can be achieved by triggering the STOP task. In this situation, a STOPPED event will be generated

when the TWI has stopped independent of whether or not a STOP condition has been generated on the

TWI bus. The TWI slave will release the bus when it has stopped and go back to its IDLE state.

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NRF52820-QDAA-R Datasheet(PDF) 328 Page - Nordic Semiconductor